[Tarantool-patches] [PATCH 5/8] raft: fix crash when received 0 term message

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

Term in raft can never be 0. It starts from 1 and can only grow.
It was assumed it can't be received from other nodes because they
do the same. There was an assertion for that.

But in raft_msg, used as a transport unit between raft nodes, it
was still possible to send 0 term. It could happen as a result of
a bug, or if someone would try to mimic the protocol but made a
mistake.

That led to a crash in the assert in debug build.

Part of #5303
---
 src/lib/raft/raft.c   | 1 -
 test/unit/raft.c      | 8 +++++++-
 test/unit/raft.result | 3 ++-
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/lib/raft/raft.c b/src/lib/raft/raft.c
index 4d07d37e5..df34d81dc 100644
--- a/src/lib/raft/raft.c
+++ b/src/lib/raft/raft.c
@@ -241,7 +241,6 @@ raft_sm_become_candidate(struct raft *raft);
 static const char *
 raft_msg_to_string(const struct raft_msg *req)
 {
-	assert(req->term != 0);
 	char buf[1024];
 	int size = sizeof(buf);
 	char *pos = buf;
diff --git a/test/unit/raft.c b/test/unit/raft.c
index dfb5f8e43..1ed8b7af7 100644
--- a/test/unit/raft.c
+++ b/test/unit/raft.c
@@ -247,7 +247,7 @@ raft_test_recovery(void)
 static void
 raft_test_bad_msg(void)
 {
-	raft_start_test(6);
+	raft_start_test(7);
 	struct raft_msg msg;
 	struct raft_node node;
 	struct vclock vclock;
@@ -280,6 +280,12 @@ raft_test_bad_msg(void)
 	   "candidate without vclock");
 	is(node.raft.term, 1, "term from the bad message wasn't used");
 
+	msg = (struct raft_msg){
+		.state = RAFT_STATE_FOLLOWER,
+		.term = 0,
+	};
+	is(raft_node_process_msg(&node, &msg, 2), -1, "term can't be 0");
+
 	raft_node_destroy(&node);
 	raft_finish_test();
 }
diff --git a/test/unit/raft.result b/test/unit/raft.result
index a63515ed3..2398bd71c 100644
--- a/test/unit/raft.result
+++ b/test/unit/raft.result
@@ -45,13 +45,14 @@ ok 1 - subtests
 ok 2 - subtests
 	*** raft_test_recovery: done ***
 	*** raft_test_bad_msg ***
-    1..6
+    1..7
     ok 1 - state can't be 0
     ok 2 - term from the bad message wasn't used
     ok 3 - node can't be a candidate but vote for another node
     ok 4 - term from the bad message wasn't used
     ok 5 - node can't be a candidate without vclock
     ok 6 - term from the bad message wasn't used
+    ok 7 - term can't be 0
 ok 3 - subtests
 	*** raft_test_bad_msg: done ***
 	*** raft_test_vote ***
-- 
2.24.3 (Apple Git-128)